This invention relates to a transmission-reception system which includes a transmission apparatus and a reception apparatus for transmitting and receiving data such as, for example, digital audio data, respectively, and a transmission apparatus, a reception apparatus and a transmission-reception method for use with the transmission-reception system.
Audio data in the form of digital data such as, for example, music data (tune data) are provided in the form of a recording medium such as a CD (Compact Disc) or an MD (Mini Disc) on which the audio data are recorded, or provided through a communication network. In recent years, audio data digitized in a format (standards) of a new category which does not belong to conventional categories are provided.
For example, audio data compatible with the DVD-Audio standards or the SACD standards are provided. The DVD is an abbreviation of Digital Versatile Disc, and the SACD is an abbreviation of Super Audio Compact Disc.
Audio data produced in accordance with the DVD-Audio standards or the SACD standards have a frequency characteristic of 100,000 Hz (Hertz) and a dynamic range of 140 dB (decibel) in the maximum. Since a conventional CD has a frequency characteristic of up to 20,000 Hz and a dynamic range of 96 dB, audio data can be provided with a very high performance through the employment of the DVD-Audio standards or the SACD standards.
The DVD-Audio standards adopt a multi-channel system so that a maker of audio data (audio information) can use, for example, an arbitrary number of channels from the channel 1 to the channel 6 to record produced audio data onto a DVD. Thus, the user can play back and enjoy sound full of presence from the DVD in a home theater or the like.
When digital audio data are transmitted between electronic equipments, taking an influence of noise in the transmission process and so forth into consideration, the digital audio data are preferably transmitted in the form of digital data without converting them into an analog signal. Therefore, also audio data provided in accordance with new standards such as the DVD-Audio standards are transmitted between electronic equipments along a digital bus.
In order to transmit digital audio data between electronic equipments connected to each other by a digital bus in this manner, the audio data to be transmitted are sectioned (divided) into units for transmission of a predetermined size, and to each of the divisional transmission units of the data, a label representative of what standards are used to produce the digital data is added. Then, the resulting data of the divisional transmission units are transmitted on the real time basis.
In the real time transmission, an equipment on the reception side receives data transmitted thereto in synchronism with the progress of transmission of data from an electronic equipment of the transmission side As described above, in the real time transmission, digital data are transmitted with a label applied thereto which indicates what standards are used to produce the digital data so that an electronic equipment of the reception side can recognize the standards for the digital data and perform suitable processing in accordance with the standards to play back the received audio data.
When it is intended to transmit main information data which are a main subject of transmission such as, for example, digital audio data on the real time basis between electronic equipments connected to each other by a digital bus, it is sometimes necessary to transmit ancillary data to the equipment of the reception side in addition to the main information data.
For example, in transmission of linear PCM audio data in accordance with the DVD-Audio standards described above, it is necessary to transmit ancillary data for allowing an equipment of the reception side to process multi-channel audio data based on the number channels of the equipment of the reception side and process the received audio data in accordance with the DVD-Audio standards to play back sound in a form estimated in advance.
The ancillary data cannot be transmitted through a single transmission process as data of a predetermined transmission unit. Accordingly, in order to transmit all ancillary data, the ancillary data must be divided and transmitted by a plural number of times for each predetermined transmission data unit. However, it is considered that, where ancillary data are transmitted by a plural number of times for each predetermined transmission data unit, a miss of some ancillary data may possibly occur.
Even if a miss of some data occurs with main information data such as audio data, this may be admitted (permitted) in the transmission process if one of various interpolation techniques is used. However, since ancillary data individually have important significance and replacement of any of them with some other data disables normal playback processing, such an interpolation technique as can be applied to audio data cannot be applied to ancillary data. Accordingly, it matters to recognize individual ancillary data of a predetermined transmission unit and assure the sequence property of the ancillary data.
To this end, it is a possible idea that an asynchronous communication system such as asynchronous communication which is used to transmit data whose miss is not permitted such as, for example, control data is used for a digital interface of the IEEE (Institute Electrical and Electronics Engineers) 1394 standards.
In particular, a reception equipment which receives data from a transmission equipment sends back a response representing the reception of the data to the transmission equipment, and when the response is received, the transmission equipment transmits next data, but when no response is received, the transmission equipment transmits the same data again so that all ancillary data may be transmitted with certainty. However, this countermeasure eliminates the real time property. On the other hand, it is cumbersome to transmit audio data and ancillary data in accordance with different transmission systems such that the audio data are transmitted on the real time basis in accordance with a synchronous communication system and the ancillary data are transmitted by asynchronous communication, and besides this increases the load to the transmission apparatus and also to the reception apparatus.
It is another possible idea to apply, for example, individually different sequenced labels to ancillary data divided into predetermined transmission units to be transmitted. This countermeasure, however, uses labels wastefully and decreases the extensibility of labels.
Further, if it is tried to apply different labels individually to ancillary data divided into predetermined transmission units, then an equipment on the transmission side must form a large number of different labels to be applied to the individual transmission units of the ancillary data and add the labels individually to the transmission units of the ancillary data. This applies a high load to the equipment of the transmission side.
Also the equipment of the reception side must recognize the ancillary data applied to the individual transmission units of the ancillary data and re-construct the ancillary data based on the recognized ancillary data. Therefore, the equipment of the reception side must use a complicated decoding circuit and a high load is imposed on the equipment of the reception side.
Therefore, it is demanded, in real time transmission of digital data whose amount is so large that they must be transmitted divisionally by a plural number of times but whose miss or drop cannot be admitted like such ancillary data as described above, to make it possible to transmit the digital data with certainty and accurately without using labels wastefully and without imposing a high load on any of electronic equipments of the transmission side and the reception side.